For convenience, the background to the present invention will be described with reference to driving of augers or drilling units. However, it will be appreciated that the drive unit of the present invention may be used in applications other than driving augers or drilling units.
Augers and drilling units are used to form holes or bores in the earth or ground. Augers typically comprise a screw flight that engages with the ground. The screw flight is connected to a drive unit and the drive unit causes rotation of the screw flight. Similarly, drilling units typically comprise a drill string that is connected to a drive unit, with the drive unit causing rotation of the drill string.
Augers and drilling units may be suspended from an arm, such as the arm of a backhoe or an arm extending from a truck or other vehicle. Larger drilling units may be mounted to a special drill rig. If the augers or drilling units are suspended from an arm, swing control systems may be utilised to control pendulation of the auger or drilling unit. A suitable swing control system is one that is sold by the present applicant and described in Australian patent number 2002240700, the entire contents of which are hearing incorporated by cross-reference.
The drive units that are used to drive augers and drilling units typically include a hydraulic motor that has an output shaft. High-pressure hydraulic fluid is provided to the hydraulic motor and this causes the hydraulic motor to rotate and drive the output shaft.
Hydraulic fluid that has passed through the motor (and is at a lower pressure relative to the inlet pressure of the hydraulic fluid fed to the hydraulic motor) is removed from the hydraulic motor. The output shaft normally meshes with a gearbox reduction drive which, in turn, is connected to the auger or drilling string to thereby cause rotation of the auger or drilling string.
Hydraulic motors comprise a motor body that houses a rotor. Opposed end plates are positioned on either side of the motor body and are joined to the motor body. Hydraulic motors are well-known to person skilled in the art and examples of suitable hydraulic motors include hydraulic motors of the “geroller” type as sold by Eaton Corporation.
In order to provide high torque drive units of the type described above, it has been common practice to provide the drive units with larger hydraulic motors that have a higher torque output. However, hydraulic motors of higher torque output can become quite large and quite expensive.
There have been some attempts in the past to provide drive units that include two or more hydraulic motors. In such drive units, the output shaft of each hydraulic motor meshes with either a drive unit output shaft or with a gearing or gearbox arrangement that drives an output shaft of the drive unit. These previous attempts have required connection of the hydraulic fluid inlets and hydraulic fluid outlets of each of hydraulic motors to appropriate hydraulic lines in order to establish proper hydraulic fluid flow to and from the hydraulic motors. Consequently, a larger number of hydraulic lines are required to connect the hydraulic motors to the source of high pressure hydraulic fluid and to the low pressure hydraulic fluid drain tank. Experience has shown that hydraulic fluid lines are prone to leakage or failure and accordingly place higher maintenance levels on to those drive units. This has the potential to cause increases in maintenance costs and increases in machine downtime due to the requirement to repair hydraulic fluid lines and hydraulic fluid line connections.
The present applicant does not concede that any of the prior art discussed in this document forms part of the common general knowledge in Australia or elsewhere.
Throughout the specification, the term “comprising” and its grammatical equivalents shall be taken to have an inclusive meaning unless the context of use indicates otherwise.